The present invention relates to vapor compression refrigeration systems which comprise a compressor, a condenser and an evaporator that are connected in a refrigeration loop. More particularly, the invention relates to a refrigerant management system which automatically adjusts the amount of refrigerant in the refrigeration loop in order to optimize the operating efficiency of the compressor motor.
Conventional vapor compression refrigeration systems include a compressor, a condenser and an evaporator that are connected together in a closed refrigeration loop. Certain typically smaller refrigeration systems are designed to operate with a fixed amount of refrigerant, and the compressor is driven at a constant speed by an electric motor that is designed to operate at or near the peak of its efficiency curve under a predetermined cooling load. The work performed by the compressor motor is a function of the mass flow rate of the refrigerant, the heat of compression of the refrigerant in the compressor and the pressure differential across the compressor. The pressure differential across the compressor in turn is related to the cooling load, that is, the difference between the ambient temperature and a desired evaporator temperature. Thus, during assembly the refrigeration loop is charged with a specific amount of refrigerant so that the work performed by the compressor motor to achieve a predetermined amount of cooling will correspond as closely as possible to the maximum operating efficiency of the compressor motor. However, as the cooling load increases or decreases, the pressure differential across the compressor will also increase or decrease, respectively, and thereby force the compressor motor to work at less than its optimal efficiency.
One way to ensure that the compressor motor operates at its optimal efficiency is to adjust the amount of refrigerant in the refrigeration loop in conjunction with the changing cooling loads. This will vary the mass flow rate of the refrigerant and therefore allow the compressor motor to continue to work at or near its optimal efficiency. Certain prior art devices have been developed to increase or decrease the amount of refrigerant in the refrigeration loop for this purpose. For example, U.S. Pat. No. 5,611,211 discloses a device which comprises a refrigerant storage vessel that is connected to the refrigeration loop and a thermal input element that can selectively heat the refrigerant in the storage vessel to expand and thereby displace the refrigerant into the refrigeration loop. However, the response times of such devices tend to be relatively slow, and the introduction of heat into the refrigeration system may be less than desirable.
In accordance with the present invention, these and other disadvantages in the prior art are overcome by providing a refrigerant management system for a vapor compression refrigeration system which comprises a compressor, a condenser and an evaporator that are connected together in a refrigeration loop through which a refrigerant is conveyed. The compressor is driven by a motor which operates at or near the peak of its efficiency curve under a first cooling load. The refrigerant management system comprises at least one sensor for generating a signal which is indicative of an actual cooling load on the refrigeration system, a controller for determining a difference between the actual cooling load and the first cooling load from the sensor signal, and a refrigerant storage device which is responsive to the controller to either remove refrigerant from or add refrigerant to the refrigeration loop.
The refrigerant storage device comprises a housing which defines an enclosure that is connected to the refrigeration loop and which includes first and second electrical conductors, a valve which is selectively activated by the controller to control the flow of refrigerant between the refrigerant loop and the enclosure, a sorbent which is positioned in the enclosure between the first and second conductors, and a power supply which is connected to the conductors and which is selectively activated by the controller. When the valve is open and the power supply is deactivated, the refrigerant will be drawn from the refrigeration loop and combine with the sorbent to form a refrigerant/sorbent compound. Furthermore, when the valve is open and the power supply is activated, the power supply will generate a current through the refrigerant/sorbent compound to desorb the refrigerant from the sorbent, whereupon the refrigerant will expand into the refrigeration loop. In this manner, when the controller detects the difference between the actual cooling load and the first cooling load, the controller will activate the refrigerant storage device to adjust the amount of refrigerant in the refrigeration loop to maintain the compressor motor operating at or near the peak of its efficiency curve.
Thus, the present invention provides a means to automatically adjust the amount of refrigerant in the refrigeration loop in conjunction with the changing cooling loads to ensure that the compressor motor will work at or near its optimal efficiency. In addition, the refrigerant storage device relies on proven adsorption and desorption processes to effect the adjustment of the refrigerant in the refrigeration loop. Moreover, since the desorption reaction is driven by an electric current, the refrigerant storage device does not rely on heat to displace the refrigerant into the refrigeration loop.
These and other objects and advantages of the present invention will be made apparent from the following detailed description, with reference to the accompanying drawings. In the drawings, the same reference numbers are used to denote similar elements in the various embodiments.